This invention relates to a wire bonder, namely, apparatus for electrically connecting by a plurality of fine electrically conductive wires or bonds a plurality of electrodes of an electronic circuit element and a plurality of leads arranged in a predetermined geometric configuration on a lead frame. The circuit element may be a pellet or chip of a semiconductor integrated circuit. The fine wires may be of gold, aluminium, or a similar material. This invention will therefore be described mainly as applied to the bonding of semiconductor pellet electrodes and leads therefor.
In the manufacture of integrated circuits, bonding requires about a half of the man hours and has therefore created a production bottleneck. Automatic wire bonders of two major types have recently been proposed.
A bonder of a first previously proposed type comprises a work stage for supporting a lead frame on which a pellet is mounted in a preselected position, a bonding tool movable relative to the work stage for carrying out the bonding operation itself, feedback means for producing signals representative of the present position of the bonding tool relative to the work stage, and a control computer system comprising, in turn, a program storage for a banding program, a position or coordinate storage for positions or coordinates for the electrodes and leads, and a central processing unit for driving the bonding tool between the programmed positions of the electrodes and leads to sequentially carry out the bonding in compliance with the program. The bonder operates on the assumption that the pellet is mounted on each lead frame in an ideal or prescheduled position with the ideal prescheduled orientation. It is therefore necessary that the mounting of a pellet on a lead frame be done with great care and that the leads have wide ends to provide a tolerance for possible misalignment of a pellet on the lead frame. The latter fact makes it impossible to apply the bonder to bonding of electrodes of a large-scale integrated circuit with closely spaced leads.
A bonder of a second previously proposed type comprises, in addition to the elements of the bonder described in the preceding paragraph, adjusting means for turning the work stage, which is now rotatable, and displacing the bonding tool relative to the work stage to cause the feedback means to produce electric signals representative of the amount of misalignment in the directions of an orthogonal rectilinear coordinate axes and in the azimuthal direction on starting the bonding. More particularly, the work stage is rotated from a position in which the lead frame is aligned with the coordinate axes to a position in which the pellet is so aligned. In addition, the bonding tool is displaced to a starting position predetermined with respect to the pellet. On carrying out the bonding at each lead, the control computer system rotates the work stage in compliance with the azimuthal error and drives the bonding tool to a position determined by the programmed position and the axial misalignment. Although the bonding is thus automatically carried out, it is necessary to rock the work stage on carrying out bonding at each of the electrodes and leads. Due to the rocking motion of the work stage of a large mass, the bonder generates considerable vibrations and must operate at a low speed. In addition, the bonder is unreliable particularly in the azimuthal direction.
Furthermore, it has been necessary with conventional automatic bonders to carry out troublesome adjustment of zero points of the feedback means upon each change of the pellets from one type to another. Such bonders also require a change from one to another of the position storages for the pellets of the respective types.